This invention relates to a pressure swing adsorption system for the simultaneous separation in a single adsorption plant of at least two crude gas streams having different compositions. The raw gas stream is considered to be any gaseous stream fed to the adsorption plant and separated therein.
In a conventional pressure swing process, several interchangeable and reversible adsorbers are employed in sequential phases: an adsorption phase and a regenerating phase, the latter comprising stages of expansion, purging, and pressure buildup. A pressure swing process for the treatment of two crude gas streams is disclosed in DOS [German Unexamined Laid-Open Application] 2,854,060, incorporated by reference herein along with the United States counterpart U.S. Pat. No. 4,280,824, issued July 28, 1981. In this reference, a feed gas for a chemical reaction is separated from a first crude gas stream in a pressure swing adsorption plant. This feed gas then enters a reaction zone wherein relatively incomplete reaction occurs resulting in a product stream having a high content of unreacted feed gas. The product gas is then recycled (as the second crude gas stream) into the adsorption plant to separate the desired product so that the unreacted proportions of the feed gas can be recycled into the reaction zone. In this conventional process, especially applicable to air fractionation and the separation of ozone from an oxygen-ozone mixture, the two crude gas streams are fed into each adsorber during different operating phases. In particular, either two successive adsorption phases or a pressure buildup phase and an adsorption phase are provided for this purpose.
On the basis of total crude gas fed to one adsorber, the loading of the adsorbers with different components from various crude gas streams results in a dilution of the component to be adsorbed from one crude gas by the other crude gas. This dilution effect in turn results in a lower loading on the adsorbent so that for the separation of a given raw gas, a larger quantity of adsorbent is required than would be the case if the separation of the different crude gas streams were conducted in two separate adsorption plants. Another disadvantage resides in the fact that all adsorbed components end up in the residual gas. Instead, it would be desirable, because in many cases the adsorbed components separated from the partial streams have divergent properties, for the components to be recovered separately.
Heretofore, these disadvantages were only avoidable if one pressure swing adsorption plant were employed for each raw gas stream.